1. Field of the Invention
This invention relates generally to formation interval straddle tools that are employed for formation zone fracturing or other formation treating operations. More particularly, the present invention concerns a tubing conveyed multi-position treating tool having xe2x80x9cSetxe2x80x9d, xe2x80x9cTreatxe2x80x9d, xe2x80x9cDumpxe2x80x9d and xe2x80x9cReleasexe2x80x9d positions which are achieved by a mechanical indexing mechanism loaded by a compressed gas or mechanical return spring, and which requires no set-down forces for actuation. Even more particularly, the present invention concerns a treating tool that is anchored by injection pressure actuated buttons and sealed to the well casing by injection pressure energized packers. This invention also concerns a treating tool which provides a bypass passage across the isolated interval to allow continuous communication between the zones above and below the straddled interval when the tool is xe2x80x9cSetxe2x80x9d or is engaged in the process of formation treating.
2. Description of Related Art
State-of-the-art coiled tubing (CT) conveyed straddle tools used for coiled tubing fracturing are generally either 1) tools with upper and lower cup packers with a single operating position (xe2x80x9cTreatxe2x80x9d), or 2) tools with an upper cup packer and a lower mechanically set squeeze packer and at most three operating positions (xe2x80x9cUnsetxe2x80x9d, xe2x80x9cSet/Treatxe2x80x9d and xe2x80x9cDumpxe2x80x9d).
Tools of the first type require reverse circulation after fracturing a zone to clean slurry left in the CT and between the cups. This is a severe limitation when low pressured zones will not allow reliable reverse circulation and due to safety issues of permitting flowback of well fluids to surface through the CT. These tools are generally limited to operation shallower than 5000 feet true vertical depth (TVD) because of the high CT swabbing forces when trying to pull-out-of-hole (POOH) after treatment since the fluid in the annulus must be lifted to surface by the lower cup. Further, the state-of-the-art in cup packer technology generally limits fracturing differentials to about 6000 pounds per square inch and to wells with measured depths (MD) less than 10,000 feet because of abrasive wear on the cups.
Recent advances in the art of formation fracturing address some of these issues. For example, a tool bypass passage that allows continuous communication from the zone above the straddle interval to the zone below limits the high swabbing forces when POOH. Further, a hydraulically operated dump valve eliminates the need for reverse circulation in some wells. However, even with these advances, operation is not permitted in severely under-pressured wells, in wells with a maximum depth greater than about 10,000 feet, or in wells where the fracturing differentials exceed 6000 pounds per square inch.
Tools of the second type have all of the limitations of the dual-cup style tool except that they can be operated in wells up to about 10,000 feet total depth (TD) since there are no high swabbing forces during POOH after the conventional squeeze packer is unset. Reverse circulation is still required because slurry will cause packer erosion if it is dumped over the squeeze packer. Additionally, the tool is limited to moderate depths because of abrasive wear on the single cup.
A mechanically operated dump valve may be combined with the mechanically operated squeeze packer so that the J-mechanism, indexing or shifting mechanism, of the tool has three positions: xe2x80x9cUnsetxe2x80x9d, xe2x80x9cSet/Treatxe2x80x9d, and xe2x80x9cDumpxe2x80x9d. The xe2x80x9cDumpxe2x80x9d Position theoretically allows pressure equalization across the squeeze packer before unsetting and dumping of slurry below the tool without reverse circulation. However, tools of this type typically do not have a bypass passage, so that fluid displaced below the fracturing tool must be forcibly displaced xe2x80x9cbullheadedxe2x80x9d into formation zones located below the tool. This practice is undesirable due to potential formation damage. Tools of this type typically use a mechanical packer that is set by applying a set-down load from the tubing that is utilized to convey and position the tool. Use of a set-down load limits operation in deep deviated wells due to helical buckling of the coiled tubing because the coiled tubing cannot normally be used for transmission of set-down loads to the tool for setting of the packer. Further, anchoring slips on a mechanically energized packer are prone to jamming due to slurry dumped to the formation zones below the tool.
It is a principal feature of the present invention to provide a treating tool which is conveyed by tubing, incorporates packers that are hydraulically energized and is capable of being shifted to any of four possible conditions or modes, xe2x80x9cSetxe2x80x9d, xe2x80x9cTreatxe2x80x9d, xe2x80x9cDumpxe2x80x9d and xe2x80x9cReleasexe2x80x9d multiple times during one trip into a well.
It is a further feature of the present invention to provide a treating tool which is shifted to its various positions or modes by hydraulically controlled positioning, thus avoiding the need for application of set-down forces for tool actuation and providing effectively for coiled tubing conveyance of the tool and coiled tubing transmitted pressure for operation of the tool.
It is another feature of the present invention to provide a novel treating tool which maintains communication of casing sections above and below the formation interval straddled by the tool during the treating process to permit interchange of fluid within the well casing and across the formation being straddled by the treating tool.
It is also a feature of the present invention to provide a novel treating tool which provides for drainage of liquid that may be collected within the tubing above the tool and to provide for flushing through the tool.
Briefly, the invention is a tubing conveyed, multi-position straddle tool for fracturing or other formation treating operations that has a tubular housing carrying anchor devices and packer elements for anchoring and sealing the tool within a well casing. An inner tubular member is in telescopically movable assembly with the tubular housing and is positionable relative to the tubular housing to define the various positions or modes of the tool. The anchors and packers do not touch the wall of the casing when not energized, e.g. squeeze-type packers. The tool shifting mechanism, e.g. J-mechanism, has four positions: xe2x80x9cSetxe2x80x9d, xe2x80x9cTreatxe2x80x9d, xe2x80x9cDumpxe2x80x9d, and xe2x80x9cReleasexe2x80x9d. The xe2x80x9cReleasexe2x80x9d mode of the tool may also be characterized as an xe2x80x9cEmergency Releasexe2x80x9d mode, which is achieved simply by applying an upward or lifting force to the inner tubular element and maintaining the lifting force until release of the tool has been accomplished. The J-mechanism is loaded in a direction opposing the lifting force by a nitrogen spring so that no set-down forces are required for actuation. The tool is anchored during operation by pressure actuated buttons at the upper end of the tool and is sealed with respect to the well casing by squeeze packers which are pressure energized. Further, a bypass passage is provided that extends through the tool to locations above and below the packers and which allows continuous communication between wellbore sections above and below the straddled interval with the tool anchored and sealed with respect to the well casing. The bypass passage permits fluid being pumped through the tool and into the casing below the tool to displace casing fluid upwardly through the tool to the casing above the tool. The treating tool is a multi-set tool which permits resetting in the downhole environment so that many formation treating activities may be accomplished without retrieving the tool from the well.
The treating tool of the present invention is capable of being indexed to its xe2x80x9cSetxe2x80x9d, xe2x80x9cTreatxe2x80x9d, xe2x80x9cDumpxe2x80x9d and xe2x80x9cReleasexe2x80x9d conditions or modes without requiring application of a set-down force to the tool. The tool is activated to its anchored and set condition within the casing by hydraulic pressure, being a differential pressure that is achieved by the flow of fluid through a setting orifice. After having been anchored and set within the casing, the setting pressure is trapped so that the anchors maintain anchoring engagement within the casing and the packers remain energized. Thereafter, pumping may be stopped without releasing the tool from its set and energized condition. Shifting or indexing of the tool to its xe2x80x9cReleasexe2x80x9d mode is achieved by applying an upward or pulling force to the inner tubular member and shifting or indexing of the tool to its xe2x80x9cSetxe2x80x9d, xe2x80x9cTreatxe2x80x9d and xe2x80x9cDumpxe2x80x9d modes is achieved by pulling upwardly on the tool to move the inner tubular member upwardly relative to the anchored and sealed tubular housing and then relaxing the pulling force to permit downward movement of the inner tubular member by the nitrogen spring or other suitable urging means. Upward and downward movement of the inner tubular member relative to the tubular housing is controlled by an indexing mechanism also known as a J-mechanism.
So that the manner in which the above recited features, advantages and objects of the present invention are attained may be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the preferred embodiment thereof which is illustrated in the appended drawings.
It is to be noted however, that the appended drawings illustrate only a typical embodiment of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.